Gale Warning 184, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
454 PM AKST Thu Feb 21 2019

.ANALYSIS AND UPPER LEVELS...
There is a fairly strong vertically stacked low over the northeast
Gulf rapidly moving east. Behind this low a ridge of high
pressure is building over southern Alaska, both at the surface and
aloft. Strong offshore winds are occurring over and near the
Southcentral coast. Most of southern Alaska is dry, but some
showers are lingering over the lower Kuskokwim Valley. There is a
large upper low over the western Bering Sea. A strong surface low
(around 970 mb) is associated with this low, and a front stretches
from the western Bering to near the Pribilof Islands, and then
south-southwest across the central Aleutians into the north
Pacific. High end gale-force winds are associated with this
front.

&&

.MODEL DISCUSSION...
The numerical models are in very good agreement across southern
mainland Alaska through Saturday afternoon. Further west, there
are some differences in how the models handle a low moving across
the central/western Aleutians Friday afternoon and then northward
across the central Bering Friday night and Saturday. The American
models (GFS and NAM) are further west, a little faster, and keep
the low strong longer than the ECMWF and Canadian GEM. In general,
forecast confidence is above normal.

&&

.AVIATION...
PANC...VFR conditions and light winds will most likely persist.
There is a chance of some fog early Friday morning, but the
likelihood is low, so it was handled with VCFG for now.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
(Tonight through Sunday)

A much quieter and less challenging forecast is in store for the
region. In general, a ridge of high pressure will develop across
southern Alaska on Friday. So while the day with start with gusty
outflow winds in the Prince William Sound and Copper River Delta
regions, these will be winding down through the day. Then, the
ridge builds eastward and repositions its center over the Kenai
Peninsula/Anchorage Bowl. This will lead to dry conditions
through the period, with the main weather concern being fog
development, as a steep low-level inversion develops by the
weekend.

For most locations, morning fog and low stratus will gradually
give way to at least some breaks in the clouds, with the exception
to this rule being across parts of the Copper Basin, where the
fog may be more dense with less potential for the stratus to scour
out during the max heating cycle (afternoon). The one challenging
part to the forecast in this pattern will be temperatures.
Depending on where fog sets up and how long it lingers through the
day can wreak havoc on maximum and minimum temperatures
(fog/stratus keeps it significantly warmer at night and colder
during the day).

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Tonight
through Sat)...A vertically stacked low centered over the Bering
Strait continues to weaken. While cold dry air from eastern
Siberia wrapping into the south side of the low could trigger
showers in the Kuskokwim Mountains this evening, most of southwest
will continue to see quiet weather and areas of blue skies until
tonight.

A ridge over the central and eastern Aleutians will maintain dry
conditions downstream, with patchy fog in Bristol Bay. Farther
north in the Kuskokwim Delta and Kuskokwim Delta Coast, expect a
transition to wetter conditions tonight. South flow ahead of a
gale force low in the Western Bering will bring increased south
winds and possible precipitation in the Kuskokwim Delta tonight
into Saturday, with precip types initially snow. Areas of blowing
snow are possible along the Kuskokwim Delta coast/Nunivak Island
tonight, but considering projected temperatures are just below
freezing and low forecast precipitation amounts, do not expect
significant impacts other than possible periods of lowered
visibility. A secondary low developing in the baroclinic zone in
the north Pacific will deepen and push northward into Saturday.
This will deepen the southerly/southwesterly fetch of warm, moist
air warming conditions to above freezing over most of the mainland
by Saturday, though any precipitation should stay offshore.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...A gale
force low roughly 250 miles north of Attu will continue to impact
the Bering Sea, Aleutians, and Pribilof Islands into Friday. The
low is weakening and shifting northward, but a secondary low
forming in the associated baroclinic zone in the north Pacific
will deepen and shift northward tonight into tomorrow. This will
support persistent southerly winds and moisture advection ahead
of the low. Precipitation will continue over the central Aleutians
into the Bering including the Pribilofs through much of Friday,
with snow in the Pribilofs changing over to rain by early
afternoon. The low will shift northeastward Saturday and the focus
of precipitation will shift to the eastern Aleutians as brief
ridging develops to the west. Another potent low will approach the
Western Aleutians Sunday.

&&

.MARINE (Days 3 through 5)...
Once again, the main area of active weather with strong wind will
be over the Bering Sea Sunday through Tuesday. Sunday begins with
a ridge extending across the eastern Bering Sea with a large
strong storm crossing the western Aleutians. This storm should
pack storm force winds on its leading edge with the potential for
a brief period of hurricane force winds possible in the Central
to Western Aleutians as well as the western Bering Sea offshore
zones. By Monday the low weakens but we should still see some
storm force winds close near the center of the low over the
Central Bering Sea with gales across much of the eastern Bering
Sea to the southwest coast. By Tuesday, this storm continues its
northward trek as yet another gale to storm force low crosses the
western and central Aleutians.

Meanwhile the Gulf of Alaska remains under high pressure and we
are not anticipating any significant wind or waves for the Gulf
region Sunday through Tuesday.

&&

.LONG TERM FORECAST (Days 3 through 7...Sun through Thu)...
For the extended period, high pressure over the Gulf of Alaska
and southern mainland will result in benign conditions for the
southern mainland. The large upper level high will likely lead to
the development of inversions through Southcentral and may result
in more foggy conditions. Also, we are expecting very warm 850 mb
(~5000 ft) temperatures over the southern mainland that could
result in some unseasonably warm temperatures along with large
diurnal fluctuations for areas that aren't trapped under an
inversion. The southwest mainland will see temperatures running 10
to 20 degrees above normal with persistent southwesterly flow
through the week.

Out west, we have a very active pattern on tap for next week. We
start off with a strong storm to hurricane force low over the
western bering and western Aleutians that treks north across the
Bering as a ridge over the eastern Bering gets pushed east over
the mainland. After this low moves out of the Bering, another
strong storm force low is on tap for the western and central
Aleutians. By the later half of the week the lows are a bit weaker
as they trek across the Aleutians and Bering Sea. A weak ridge
pokes up across the central Aleutians to the eastern Bering Sea
Friday. Lastly, another storm force low will impact the western
Aleutians and western Bering Sea Saturday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 131.
MARINE...Storm Warning 131
		 Gale Warning 411-414 165 170 172-185 351 352 119 120 121
                      127 128 130 132 137
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...SA/KVP